As is known, patterning of polymer thin films on topography has many applications in the fabrication of micro-electromechanical systems (MEMs) or electronic devices, such as those being used to cap micro- or nanometer-sized features or to form multi-layer structures in organic light-emitting diodes (OLEDs). However, conventional patterning methods, such as nanoimprint lithography (NIL) or microcontact printing (μCP), have many limitations. These processes produce patterns on flat surfaces. It is not only hard to form a continuous film over topography, but also very difficult to pattern films either inside trenches or on protrusions of topography 18.
As seen in U.S. Pat. Nos. 5,512,131 and 6,180,239, a method of patterning a material surface using a PDMS pad is provided, wherein a chemical species capable of forming a self-assembled monolayer (SAM) is coated onto the padding surface of the elastomer pad. The padding surface is placed against another surface of a material and removed to leave a SAM of the species according to the surface pattern of the pad.
According to the present invention polymer and a flat PDMS pad are used for patterning, rather than a SAM and a patterned PDMS stamp. Advantages of using a flat PDMS pad, instead of a patterned PDMS stamp, lie on the easiness of coating a smooth film and the prevention of sagging or pairing among stamp features. The use of polymers provides several advantages as well. Firstly, they may have tunable film thickness, higher etch resistance and large selection of material properties (electronic, optical, or mechanical). Secondly, polymers are not only patternable onto flat or curved surfaces, but also onto surfaces with patterns. The latter is highly desired for creating 3-D structures in micro-electromechanical systems (MEMS) and construction of organic optoelectronics. Lastly, the patterns on topography of the present invention are achieved through controlled deformation of a PDMS pad on a topography, not through chemical bonding.
It is also known to pattern a polymer film on a smooth substrate, instead of a patterned substrate as in the present invention. In the prior art process, a thin film of polymer is first deposited on a smooth substrate and the patterning takes place by applying a PDMS pad in conformal contact to the film, such that protruding elements of the pad are attached to the material surface. In contrast, polymer films according to the present invention are deposited on PDMS directly.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.